Drop platform structure for a loading dock

ABSTRACT

A drop platform structure for use with a loading dock is provided including a pair of elongated telescoping frame members, one of the members being pivotally secured to the dock and the other member being pivotally secured to a brace which is also pivotally secured to the dock. An elongated platform is slidably disposed with respect to the frame members and, upon retraction thereof, automatically telescopes the frame members so as to raise them from a generally horizontal to a generally vertical position.

United States Patent Lapham 5] Oct. 24, 1972 [54] DROP PLATFORM STRUCTURE FOR A LOADING DOCK [72] Inventor: Sidney D. Lapham, 2324 Tice Creek Dr., Walnut Creek, Calif. 94595 [22] Filed: March 15, 1971 [211 Appl. No.: 124,050

[52] US. Cl ..l4/7l [51 1 Int. Cl ..B65g 11/00 [58] Field of Search 14/71 [56] References Cited UNITED STATES PATENTS 2,527,653 10/1950 Pierce ..l4/7l 3,0l8,496 l/l962 Hosbein ..l4/7l 3,581,332 6/197] Van Marle ..14/7l Primary ExaminerJacob L. Nackenoff AtrorneyMellin, Moore & Weissenberger ABSTRACT 10 Claims, 8 Drawing Figures PATENTEU BW m2 9999.599

SHEET 2 Bf 3 INVENTOR SIDNEY D. LAPHAM ATTORNEYS DROP PLATFORM STRUCTURE FOR A LOADING DOCK BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to loading docks; and, more particularly, to a drop platform for use with a loading dock or the like to provide access to an adjacent tank car or the like.

2. Description of the Prior Art In order for an operator to gain access to a tank car when it is parked alongside a loading dock, it is necessary to swing a platform down from the loading dock over to the catwalk of the tank car so that the operator can walk over the platform to the dome of the tank car and actuate appropriate loading and operating mechanisms. Known prior art platforms have proven unreliable in use and extremely complicated in mechanism. This is especially true when such platforms are to be used in conjunction with tank cars having corrosive chemical fumes associated therewith, such fumes tending to interfere with the proper functioning of the operating mechanism of such prior art platforms (these operating mechanisms being generally hydraulic or the like). There is a need for a reliable and relatively simple arrangement for raising, lowering, extending and retracting such platforms to any desired position in any type of environment.

SUMMARY OF THE INVENTION It is an object of this invention to provide a drop platform structure for use with a loading clock that operates efficiently in any type of environment.

It is a further object of this invention to provide a drop platform structure having relatively few moving parts which can be raised, lowered, extended and retracted to any desired position.

These and other objects are preferably accomplished by providing a pair of elongated telescoping frame members, one of the members being pivotally secured to a loading dock and the other member being pivotally secured to a brace which is also pivotally secured to the dock. An elongated platform is slidably disposed with respect to the frame members and, upon retraction thereof, automatically telescopes the frame members so as to raise them from a generally horizontal to a generally vertical position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical, partly sectional, view of a preferred platform structure in accordance with my invention;

FIG. 2 is a partly sectional plan view, with portions omitted for convenience of illustration, of the arrangement of FIG. 1;

FIG. 3 is a vertical, partly sectional, view similar to FIG. I with portions omitted therefrom showing the means for raising and lowering the platform structure of FIG. 1;

FIG. 4 is a view taken along the lines 4-4 of FIG. 1;

FIGS. 5 and 6 are schematic views showing the operation of the platform structure of FIGS. 1 through FIG. 7 is a detailed partly sectional view of a portion of the arrangement of FIGS. 1 and 3; and

FIG. 8 is a view taken along lines 8-8 of FIG. 3 with portions thereof broken away for convenience of illustration.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawings, a portion of a loading clock 10 is shown having a platform structure 11 pivotally attached thereto. Platform structure 11 includes a pair of elongated inner and outer telescoping frame members 12 and 13, respectively. These frame members 12 and 13 may be hollow as shown or U- shaped, or any suitable configuration for carrying out the invention as will be discussed in detail hereinbelow.

Inner frame member 12 is pivotally attached to dock 10 at point A. Such attachment may be directly on dock 10 or on a suitable carriage structure 14 as shown so that the entire carriage structure 14, including platform structure 11, may be moved longitudinally of the clock 10. This may be accomplished by providing a track 15 or the like having upper and lower momentbearing roller means 16 and 16' thereon. Carriage structure 14 includes a bracket member 17 having upper and lower portions 17 and 17" which engages roller means 16 and 16', respectively, on track 15 as shown so that the entire structure 14 may be moved longitudinally with respect to clock 10. A weight-bearing roller means 16'' may be connected to lower portion 17' to assist in movement of structure 14.

A brace member 18 is pivotally secured at one end to carriage structure 14 at pivot point B and at its other end to a bracket 9 upstanding from outer frame member 13 at pivot point C. Pivot point B is vertically above and spaced from pivot point A; however, pivot point B is preferably offset with respect to pivot point A, i.e., inwardly toward dock 10, as shown, for reasons to be discussed further hereinbelow.

As can best be seen in FIG. 2, a mast 20 extends through both inner and outer frame members 12 and I3 and is also pivotable about pivot point A. A first pair of sprockets 21 and 21' are located at pivot point A and a second pair of sprockets 22 and 22' are mounted on a sprocket support bracket 27 secured to the outer end of mast 20. A pair of control chains 28 and 28' extend about sprockets 21, 21 and 22, 22", respectively (chain 28 being shown in dotted lines in FIG. I). As can best be seen in FIG. 3, control chains 28 and 28' are secured to a pair of blocks 23 and 24 (only chain 28 being visible). Block 23 is secured to outer frame member 13, while block 24 is only secured to chain 28. Although only a single control chain is required, duplicate chains are provided for safety reasons.

The overall length of platform structure 11 may be varied by means of extendable walkway in the form of an elongated tongue member 25. Tongue member 25 telescopes into and thus is extendable and retractable with respect to inner and outer frame members 12 and 13. Tongue member 25 is so configured that it is supported within hollow members 12 and 13. The selective extension and retraction thereof is accomplished by a drive chain 26 running about a pair of sprockets 29 and 30 (FIG. 2). Sprocket 29 is located at pivot point A. That is, sprocket 29 may be secured to a shaft 31 extending through pivot point A with sprockets 21, 21' and 29 mounted on each side of mast 20 (which is pivotable about shaft 31). Shaft 31 in turn is fixed to a pair of brackets 32 and 33 extending from carriage structure 14. Sprocket 30, on the other hand, is secured to a shaft 34 fixedly mounted on support bracket 27 and a bracket 35 fixedly secured to mast 20. Conventional nuts 36 and 37 are threaded onto the free ends of shaft 34 for securing the shaft 34 in place. A similar arrangement is used to secure sprocket 22 to bracket 27 (i.e., a shaft 34' is bolted to a bracket 35' secured to mast 20 and to bracket 27 as shown through means of nuts 36', 37).

The point of connection of tongue member 25 to drive chain 26 is shown in FIG. 8. This is accomplished by providing a block 61 which is secured to both tongue member 25 and chain 26. Thus, movement of chain 26 is transmitted to tongue member 25 by means of block 61.

Referring back to FIG. 1, and with particular reference to FIG. 4, a conventional reversible drive motor 38 drives a sprocket 39 having chain 40 thereabout which extends to sprocket 41 (FIG. 2) for driving sprocket 29 which is integrally connected thereto. Motor 38 is preferably fixedly secured to a floor plate 42 or the like having upstanding brackets 43 and 44 forming part of carriage structure 14.

Referring back to FIG. 3, chain block 24 includes a pin 45 thereon extending normal thereto (i.e., normal to the direction of travel of chain 28). A block 46 is fixedly secured to the inner end of tongue member 25 through bolt means 47 and 47'. Block 46 includes a notch 48 for receiving pin 45 therein. The end of block 46 adjacent dock is preferably generally tapered, as at tapered portion 49, in a direction leading to notch 48 to assist in the engagement of pin 45 therein.

The operation of platform structure 11 will now be described. Carriage structure 14 is moved by means of track and bracket member 17 to a desired location along dock 10. As can be seen schematically in FIGS. 5 and 6 (wherein various elements are shown in a nonaligned position for illustration only), if the distance between pivot points A and C is lengthened by telescoping the two platform frame members 12 and 13 away from one another, the entire platform structure 11 will swing from a generally horizontal (FIG. 5) to a generally vertical position (FIG. 6) about pivot points A and B. Likewise, when the frame members 12 and 13 are telescoped into one another, the platform structure 1 1 will return to the horizontal position.

The telescoping of frame members 12 and 13 is accomplished by actuating motor 38, which drives sprocket 39. Chain 40 is coupled to both sprocket 39 and sprocket 41. Sprocket 41 is integral with drive chain sprocket 29 which in turn drives chain 26 and thus block 61. In this manner, tongue member 25 is selectively extended and retracted within inner and outer frame members 13.

Whenever it is desired to raise the platform structure 11 from an extended horizontal position (FIG. 5) to the retracted vertical position of FIG. 6, motor 38 is actuated to retract tongue member 25. At first, tongue member 25 merely telescopes into the two platform frame members 12 and 13. Eventually, however, the tapered portion 49 of block 46, connected to member 25, engages pin 45 connected to block 24 until pin 45 is locked into notch 48 of block 46. Since control chain 28 is also connected to block 24, chain 28 is automatically driven by the retraction of tongue member 25. This causes the chain 28 to rotate about sprockets 21 and 22 in the direction for extending platform frame members 12 and 13 (since outer frame member 13 is secured to block 24, which is also secured to and thus driven by chain 28). Depending upon the particular length of tongue member 25 and its extent of retraction into members 12 and 13, and, of course, the particular preselected location of the various components, this engagement causes platform structure 11 to rotate about pivot point A (with brace member 17 of course rotating about pivot point B), which raises the entire 5 structure to the vertical position of FIG. 6. At this point, preferably the entire length of tongue member 25 is completely retracted into platform frame members 12 and 13. In this vertical position, it can be seen that pivot point B is preferably set backa short distance beyond the vertical toward the inside of loading dock l0.

Whenever it is desired to lower and extend platform structure 11, that is, move it from its vertical (FIG. 6) to its horizontal position (FIG. 5), the foregoing steps are reversed with the following additional factors coming into play. Inasmuch as it is desirable to swing the platform structure 11 as far away from an adjacent tank car as possible, its raised position is actually a little beyond the vertical toward the inside of loading dock 10 as discussed hereinabove. It is therefore necessary to swing platform structure 1 1 under power outwardly about pivot point A until it has passed the vertical far enough for gravity to take over. For this reason, a keeper 50 is provided on shaft 31 (see FIG. 3) extending in the direction of chain 38. Block 24, connected to chain 38, includes a recess 51 for preventing pin 45 from disengagement from notch 48 while the platform structure 11 is being moved back to its horizontal position. In other words, upon retraction of tongue member 25 and subsequent movement of block 24, keeper 50 enters recess 51 and maintains pin 45 within notch 48 as structure 11 is moved to its vertical position. Upon downward movement of structure 11, keeper 50 prevents disengagement of pin 45 from notch 48 until platform structure 11 approaches the range of the generally horizontal position in which it is to be used. Block 24 further includes an outwardly and downwardly extending guide member 52 for aligning keeper 50 within recess 51.

Thus, when drive motor 38 is actuated, tongue member 25 is extended within frame members 12 and 13, block 24, through pin 45, telescopes the platform frame members 12 and 13 into one another, the disengagement of pin 45 from notch 48 being prevented by keeper 50 in recess 51. When platform structure 11 reaches some desired position from the horizontal, as for example, approximately 30 therefrom, the block 24 reaches the end of keeper 50 and pin 45 disengages from block 24. However, by this time gravity pulls platform structure 11 downwardly. The downward movement of platform structure 11 may be prevented by a pawl-and-ratchet arrangement which will now be described.

Referring to FIG. 7, a pawl 53 is pivotally attached at 54 to carriage structure 14. Pawl 53 is adapted to engage the ratchet 55 of ratchet wheel 56, which is coupled to control chain sprocket 21 (FIG. 2). Thus, as wheel 56 is rotated in the direction of arrow 57 (FIG. 7), i.e., by the upward movement of structure 1 1, pawl 53 is disengaged from ratchet 55. The engagement of pawl 53 and ratchet 55 may be accomplished by any suitable operator-controlled mechanism. Thus, when pawl 53 engages ratchet 55, the platform structure 11 can no longer move downwardly under the force of gravity and pin 45 disengages from block 23. Further extension of tongue member 25, through drive chain 26, causes tongue member 25 to simply telescope further out of platform frame members 12 and 13 until the overall length of platform structure 11 is extended to its desired length. The plurality of notches of ratchet 55 permits the angularity of structure 11 to be varied with respect to the horizontal.

When it is desired to raise platform structure 11, pawl 53 ratchets over ratchet 55 and does not affect the functioning of the structure I 1. However, since engagement of pawl 53 with ratchet 55 may jam the mechanism during this portion of operation, a cam 58 (FIG. 7) is provided on sprocket 21 at pivot point A which is adapted to engage a pawl lock-out lever 59 (see also FIG. 3) fixedly secured to pawl 53 so as to prevent pawl 53 from engaging ratchet 55 when keeper 50 holds pin 45 within notch 48.

In order to reduce the load on motor 38 while platform structure 11 is being raised, conventional counterbalance springs (not shown) may be provided in platform structure 11. Such springs may be selected and disposed to provide a lower limit to the operating range of structure 11 by preventing further movement thereof when it reaches a predetermined angle with respect to the horizontal and the springs bottom.

The control mechanism for platform structure 11 may be designed so that pawl 53 does not engage ratchet 55 as long as platform structure 11 is being lowered, but rather only when it is raised again following a lowering operation. Thus, the operator first engages the pawl lock-out lever 59 to disengage pawl 53 from ratchet 55 and lowers platform structure 1] beyond the desired level thereof through actuation of motor 38 by suitable control means (not shown). The operator then reverses motor 38 to raise platform structure 11, whereupon pawl 53 immediately engages and ratchets in ratchet 55 until the desired level is reached. At this point, the operator once again reverses motor 38 to lower platform structure 11. However, since pawl 53 is now engaged in ratchet 55, the platform structure 1 1 will not lower any further but will extend. When it has reached its desired length, motor 38 is shut off and the platform structure 11 is ready for use. After completion of work, the platform structure 1 l is again raised by reversing motor 38, which retracts tongue member 25 until block 46 engages pin 45 as discussed hereinabove. At this point, platform structure 11 will begin to raise to its vertical position while tongue member 25 continues to retract and telescopes members 12 and 13.

Suitable railings and safety chains or the like (not shown) may also be provided on platform structure 11, as is well known in the art.

I claim as my invention:

1. A drop platform structure for use with a loading dock or the like, comprising:

a pair of elongated telescoping inner and outer frame members, the inner frame member being pivotally secured at a point located on said dock and the other of said frame members being pivotally secured to a brace member pivotally secured at a second point located on said dock, said second point being spaced from and above said first point;

normally inactivated first drive means associated with said frame members for telescoping one of said frame members with respect to the other;

an elongated extensible tongue member slidably disposed with respect to said frame members;

second drive means associated with said tongue member for selectively extending and retracting said tongue member with respect to said telescoping frame members; and

means associated with both said tongue member and said first drive means for activating said first drive means during the retraction of said tongue member with respect to said telescoping frame members upon actuation of said second drive means so as to raise said frame members from a generally horizontal to a generally vertical position.

2. The platform structure of claim 1 wherein said frame members are hollow and said tongue member is slidably disposed inside of said frame members.

3. The pladorm structure of claim 1 wherein the pivot point of said brace member on said dock is spaced inwardly a short distance toward said dock from the vertical with respect to said first-mentioned pivot point.

4. The platform structure of claim 1 wherein said normally inactivated drive means includes an elongated mast pivotally mounted at said first-mentioned pivot point and extending within said telescoping frame members, said mast including at least a pair of sprockets, one of said sprockets being disposed at the end of said mast pivotally mounted to said dock and the other of said sprockets being secured to the free end of said mast, and a control chain engaging said sprockets, one end of said control chain being secured to said outer frame member and the other end of said chain being secured to a first block movable within said frame members;

said means associated with both said tongue member and said first drive means including a second block fixed to the end of said tongue member interior of said frame members and forwardly of said first block in a direction away from said first-mentioned pivot point; said means associated with both said tongue member and said first drive means further including selectively engageable portions on each of said blocks whereby upon activation of said second drive means and retraction of said tongue member, said second block engages said first block to thereby move said first block to drive said control chain and thus extend said outer frame member connected to said control chain to thereby raise said frame members to their substantially vertical position.

5. The platform structure of claim 4 wherein said selectively engageable and disengageable portions on each of said blocks include a pin integral with said first block extending in a direction substantially normal to the direction of travel of said control chain and a notch on said second block for receiving said pin therein.

6. The platform structure of claim 4 wherein said second drive means includes a reversible motor, a first drive chain driven by said reversible motor and a third sprocket in driving engagement with said first drive chain, said third sprocket being integral with a fourth sprocket pivotally mounted at said first-mentioned pivot point, and a second drive chain in driving engagement with both said tongue member and said fourth sprocket.

7. The platfonn structure of claim 5 including keeper means associated with both said dock and said second block for retaining said pin in said notch during extension of said tongue member upon movement of said frame members from a substantially vertical to a sub- 

1. A drop platform structure for use with a loading dock or the like, comprising: a pair of elongated telescoping inner and outer frame members, the inner frame member being pivotally secured at a point located on said dock and the other of said frame members being pivotally secured to a brace member pivotally secured at a second point located on said dock, said second point being spaced from and above said first point; normally inactivated first drive means associated with said frame members for telescoping one of said frame members with respect to the other; an elongated extensible tongue member slidably disposed with respect to said frame members; second drive means associated with said tongue member for selectively extending and retracting said tongue member with respect to said telescoping frame members; and means associated with both said tongue member and said first drive means for activating said first drive means during the retraction of said tongue member with respect to said telescoping frame members upon actuation of said second drive means so as to raise said frame members from a generally horizontal to a generally vertical position.
 2. The platform structure of claim 1 wherein said frame members are hollow and said tongue member is slidably disposed inside of said frame members.
 3. The platform structure of claim 1 wherein the pivot point of said brace member on said dock is spaced inwardly a short distance toward said dock from the vertical with respect to said first-mentioned pivot point.
 4. The platform structure of claim 1 wherein said normally inactivated drive means includes an elongated mast pivotally mounted at said first-mentioned pivot point and extending within said telescoping frame members, said mast including at least a pair of sprockets, one of said sprockets being disposed at the end of said mast pivotally mounted to said dock and the other of said sprockets being secured to the free end of said mast, and a control chain engaging said sprockets, one end of said control chain being secured to said outer frame member and the other end of said chain being secured to a first block movable within said frame members; said means associated with both said tongue member and said first drive means including a second block fixed to the end of said tongue member interior of said frame members and forwardly of said first block in a direction away from said first-mentioned pivot point; said means associated with both said tongue member and said first drive means further including selectively engageable portions on each of said blocks whereby upon activation of said second drive means and retraction of said tongue member, said second block engages said first block to thereby move said first block to drive said control chain and thus extend said outer frame member connected to saiD control chain to thereby raise said frame members to their substantially vertical position.
 5. The platform structure of claim 4 wherein said selectively engageable and disengageable portions on each of said blocks include a pin integral with said first block extending in a direction substantially normal to the direction of travel of said control chain and a notch on said second block for receiving said pin therein.
 6. The platform structure of claim 4 wherein said second drive means includes a reversible motor, a first drive chain driven by said reversible motor and a third sprocket in driving engagement with said first drive chain, said third sprocket being integral with a fourth sprocket pivotally mounted at said first-mentioned pivot point, and a second drive chain in driving engagement with both said tongue member and said fourth sprocket.
 7. The platform structure of claim 5 including keeper means associated with both said dock and said second block for retaining said pin in said notch during extension of said tongue member upon movement of said frame members from a substantially vertical to a substantially horizontal position.
 8. The platform structure of claim 7 including downward movement limiting means associated with both said dock and said inner frame for limiting the downward movement of said frame members.
 9. The platform structure of claim 8 including means associated with said dock for disengaging said downward-movement limiting means when said keeper means is retaining said pin within said notch.
 10. The platform structure of claim 1 including a carriage structure associated with said dock, said carriage structure being movable longitudinally of said dock, and said first-mentioned pivot point being disposed on said carriage structure. 